CN108372374B

CN108372374B - Method and device for refining crystal grains in additive manufacturing

Info

Publication number: CN108372374B
Application number: CN201710003778.1A
Authority: CN
Inventors: 单飞虎; 巩水利; 张升; 刘琦
Original assignee: AVIC Manufacturing Technology Institute
Current assignee: AVIC Manufacturing Technology Institute
Priority date: 2017-01-04
Filing date: 2017-01-04
Publication date: 2020-01-14
Anticipated expiration: 2037-01-04
Also published as: CN108372374A

Abstract

The invention relates to a method for refining crystal grains in additive manufacturing and a device thereof, and the method is characterized in that a method for stirring semi-solid formed blanks is adopted in the melting additive manufacturing process, dendrites/dendrites are crushed, the nucleation rate is increased, the crystallization rate is improved, the crystal grains are refined, the blanks are constrained in a manner of synchronously combining shaft shoulder shape following constraint on two side surfaces and the vertical direction, the problems that the blanks flow and deviate from a digital model in the stirring process or the forming is discontinuous due to stirring and the like are prevented, and the side surface shape following constraint and the stirring motion synchronously advance along with the additive manufacturing motion. The invention can realize the additive manufacturing of complex parts made of difficult-to-form materials with stable performance, high efficiency, high precision and low cost.

Description

Method and device for refining crystal grains in additive manufacturing

Technical Field

The invention relates to a method and a device for refining grains in additive manufacturing, and belongs to the technical field of additive manufacturing/welding.

Background

The design and manufacturing concepts of aerospace parts tend to be developed more and more towards the trend of light weight, long service life and low cost. The conventional production and manufacturing of parts are mainly completed by the conventional casting, forging and welding methods, which makes the product have contradictions between difficult weight reduction, long period, high cost and the like and contradictory with the design concept and cost budget, so that it is necessary to develop and research an efficient alloy design and manufacturing method and equipment manufacturing technology considering the multiple constraints of weight, service life, cost, period, materials, processes and the like.

The existing plasma arc/electric arc fuse additive manufacturing and electron beam fuse additive manufacturing can realize integrated multi-batch and small-batch high-efficiency low-cost manufacturing of larger components due to high production efficiency, the melting additive manufacturing technologies mainly rely on a heat source 13 to melt metal filling materials for direct cladding to realize additive manufacturing, the product structures of the melting additive manufacturing technologies are generally cast dendrites/dendrites and equiaxed crystal mixed structures, macroscopically obvious coarse dendrites/dendrites and microscopically anisotropic structures, and the defects of coarse grains, obvious anisotropic structures and the like in the forming process are key technologies needing to be broken through in the research and additive manufacturing of domestic key scientific research institutions and colleges.

In addition, in the field of micro-casting forging, the front side single-roll rolling or the front side hammer forging is adopted, the forging pressure is insufficient in the manufacturing process, the complete forging is difficult, and fur cracking and the like can be generated when the forging pressure is too large. If the ultrasonic wave/electromagnetic wave is adopted to oscillate a molten pool or slightly forge a forming surface, the molten pool is melted in the next remelting process and cannot form a substantial effect on grain refinement due to the small action force and the limited action area.

The problems are determined by the inherent thermodynamic, kinetic and geometrical characteristics of unconstrained free micro-casting deposition forming under the conditions of mobile heat and mass transfer because of the lack of a more thorough grain refinement link, and are difficult to be fundamentally solved only by means of ways of changing material components, process parameters and the like. The method mainly adopted for refining the crystal grains at present comprises the following steps: the above methods of grain refinement all achieve certain effects, but still have the problems of low efficiency, low forming precision and the like.

Based on the above technical problems, there is a need to create and develop an additive manufacturing technique that solves the problems of forming quality and texture of directly formed high-performance metal parts.

Disclosure of Invention

The invention provides a method and a device for refining crystal grains in additive manufacturing, aiming at the technical problems of high performance, long traditional manufacturing process of melting additive-formed metal components, high energy consumption, difficulty in stably and reliably achieving the performance of the current directly-formed products to the level of forgings, low surface quality, practical bottleneck of additive manufacturing technology and the like. The method can generate continuous stirring effect in the forming process, can effectively stir the dendrites, increase nucleation, greatly reduce the dendrite/dendrite tendency of additive manufacturing, and effectively improve the forming precision and the utilization rate of materials due to the shape following constraint of the side surface. The invention can realize the additive manufacturing of the complex parts made of the difficult-to-form materials with stable performance, high efficiency and low cost.

In order to solve the technical problems, the invention is realized by the following scheme:

in the melting and material increase manufacturing process, a method of restraining and stirring semi-solid blank by an external shaft shoulder is adopted to stir and crush the support crystal, increase the nucleation rate, improve the crystallization rate, refine the crystal grains, and meanwhile, combine the shape following restraining mode of two side surfaces to restrain the blank, so that the blank is prevented from flowing and deviating from a digital model in the stirring process, and the shape following restraining and stirring motion of the side surfaces synchronously advance along with the material increase manufacturing motion.

In a preferred technical scheme, the side surface shaping and beam forming are carried out in a roller + flat plate mode.

The shape following constraint mode adopts a roller and a flat plate to form a lateral constraint unit, and the roller aims to be constrained on one hand and can be synchronously pushed forward along with the additive manufacturing process on the other hand. The constraint space is different due to the digital model, the forming material and the forming process; the specific size of the constraint unit is different with the space size (length, width, single-side curvature and the like) of the forming component, and the specific application can adopt a mode of adding a constraint unit library to realize gapless replacement. The combination of the roller and the flat plate is adopted in the prior art.

In a preferred embodiment, the melting is carried out using a plasma arc, an electric arc or electrons as heat source.

In a preferred technical scheme, the additive material is a metal strip or wire.

In a preferred technical scheme, the stirring is performed in a mode that a shaft shoulder is used for restraining a stirring pin 14, a side surface shape following restraining plate is used for side surface shape following restraining, the melting point of a material selected by the stirring pin 14 needs to be higher than the melting point of a forming metal by at least 500 ℃, the side surface restraining plates on two sides are symmetrically arranged, force is applied equivalently, and the fixed end surface is higher than a blank by 0.5-20 mm synchronously; the digifax requires the width of the forming surface and the molten metal strip meets the additive manufacturing requirements.

In a preferable technical scheme, when the stirring mode is that the shaft shoulder restrains the stirring pin 14, the diameter of the stirring pin 14 can adopt a phi 0.1-10 mm spiral stirring pin 14. The diameter of the stirring pin 14 is selected to be related to the stirring material, the stirring depth and the blank width; the stirring needle 14 can be in a column shape or in a cone shape, and is realized by the column ▌ shape or the cone ▲ shape; the stirring depth is about 1.2-1.5 times of the current forming thickness, and the stirring speed needs to be controlled to ensure that excessive flash cannot exist while the crushed crystal is crushed.

The invention also provides a device for refining the crystal grains in the additive manufacturing, which is characterized in that: the device comprises a forming substrate 2, an additive forming blank heat source 3, a single-pass forming blank 6, a left restraint plate 15, a left driving roller 7, a left restraint plate guide unit 17, a right restraint plate 4, a right driving roller 5, a right restraint plate guide unit 16, a heat source center and a stirring device; the stirring device comprises a stirring needle 14, a stirring rotating shaft 9, a stirring shaft shoulder 11, a stirring shaft shoulder pressing plate 12 and shaft shoulder auxiliary pressing plate supports 8, the stirring needle 14 rotates synchronously with the stirring shaft shoulder 11 along with the stirring rotating shaft 9, the two shaft shoulder auxiliary pressing plate supports 8 rigidly fix the relative position degree between the shaft shoulder pressing plate and the stirring rotating shaft 9, the stirring shaft shoulder pressing plate acts on the upper surface of a single-channel formed blank 6, the stirring shaft shoulder pressing plate blank is not wetted, and the rigid constraint condition is met; the additive forming blank heat source 3 is arranged on the forming base plate 2, the single-channel forming blank 6 is arranged on the additive forming blank heat source 3, the left restraining plate 15 and the right restraining plate 4 are symmetrically arranged on two sides of the single-channel forming blank 6, the left restraining plate 15 can move along the additive manufacturing direction under the driving of the left driving roller 7 and the guiding of the left restraining plate guiding unit, and the right restraining plate 4 can synchronously advance along the additive manufacturing direction along the additive manufacturing movement under the driving of the right driving roller 5 and the guiding of the right restraining plate guiding unit; the stirring motion of the stirring device advances synchronously with the additive manufacturing motion; a heat source 13 is provided at the end of the single pass of the formed blank 6.

In a preferred technical scheme, the rollers are multiple and are uniformly distributed in the additive manufacturing direction.

The invention has the following technical effects:

(1) the invention can generate continuous stirring action in the forming process, can effectively stir and crush the dendrites, increase nucleation, greatly reduce the dendrite/dendrite tendency of additive manufacturing, and effectively improve the forming precision and the utilization rate of materials by side constraint.

(2) The method of stirring the semi-solid blank is adopted in the melting additive manufacturing process, so that the high-efficiency and high-precision additive manufacturing with synchronous shape following is realized, the additive manufacturing forming precision and the material utilization rate are improved, and the blank is restrained from deviating from a digifax by flowing in the stirring process; the stirring aims at crushing the dendrite/dendrite, increasing the nucleation rate, improving the crystallization rate and refining the crystal grains.

Drawings

FIG. 1 is a diagram of a device for refining grains by constrained stirring;

FIG. 2 is a front view of a device for grain refining by constrained stirring;

FIG. 3 is a top view of a device for grain refinement by constrained stirring;

fig. 4 is a partially enlarged view of fig. 3.

In the figure: 1-additive manufacturing direction; 2-forming a substrate; 3-additive forming blank heat source; 4-right side restraint plate; 5-right side driving roller; 6-single-pass forming of blanks; 7-left side drive roller; 8-supporting the shaft shoulder auxiliary pressure plate; 9-stirring rotating shaft; 10-stirring rotation direction; 11-stirring shaft shoulder; 12-stirring shaft shoulder pressing plate; 13-a heat source; 14-a stirring pin; 15-left side restraint panel; 16-right side restraint plate guide unit; 17-left binding plate guide unit; 18-heat source center; 19-the center distance between the stirring pin and the heat source; 20-stir pin position; 21-the distance between the front edge of the right restraint plate and the front edge of the roller; 22-right side restraining force; 23-left side restraining force; 24-the center distance between two adjacent uniformly distributed driving rollers; 25-layer 1 additive manufacturing; 26-layer 2 additive manufacturing; 27-nth layer single pass forming blank.

Detailed Description

The method and apparatus for refining grains in additive manufacturing according to the present invention will be further described with reference to the following embodiments and the accompanying drawings, but the present invention is not limited thereto

Example 1

A method for refining crystal grains in additive manufacturing is characterized in that a shaft shoulder constraint stirring pin 14 is adopted to stir semi-solid blanks in the melting additive manufacturing process, dendritic crystals are crushed, the nucleation rate is increased, the crystallization rate is increased, the crystal grains are refined, the blanks are constrained in a form of constraint along with the shape of the side surfaces of two sides synchronously, the blanks are prevented from flowing and deviating from a digital model in the stirring process, and the constraint along with the shape of the side surfaces and the stirring motion synchronously advance along with the additive manufacturing motion.

The high-efficiency high-precision additive manufacturing with synchronous shape following is realized by adopting a method of stirring the semi-solid blank by using the shaft shoulder constraint stirring pin 14 in the melting additive manufacturing process; the purpose is as follows: the additive manufacturing forming precision and the material utilization rate are improved, and the blank is restrained to prevent the blank from flowing and deviating from a digital model in the stirring process; the purpose of stirring is to crush the dendrites, increase the nucleation rate, improve the crystallization rate and refine the grains; wherein melting (plasma/arc/electron beam) is used as the heat source 13 for starting the arc; the additive material is a metal strip (wire material can be used), the forming surface width of a forming die is required to be 5mm, the molten metal strip (the width is 6mm, the thickness is 3mm) meets the additive manufacturing requirement, and the side surface shape following constraint mode is carried out by adopting a roller and flat plate mode;

the melting point of the material selected by the stirring pin 14 needs to be at least 500 ℃ higher than the melting point of the forming metal, the principle of the stirring head is that the hardness and the high-temperature strength of the stirring head are higher than those of the material to be processed, the stirring head can be made of tool steel materials or hard alloy materials, the stirring pin 14 is made of the material to be processed

A spiral stirring pin 14, the stirring depth is about 1.2-1.5 times of the forming thickness of the current forming; the stirring speed needs to be controlled to ensure that the support crystal is crushed and excessive overflowing cannot occur at the same time. The width of the shaft shoulder is 1-3mm narrower than the shape following restraining plates on the left side and the right side, and is 3-5 times of the diameter D of the stirring needle 14; the length of the shaft shoulder is 70-80% of the length of the restraint plate, and the installation position starts from the tail part of the molten pool. The thickness can meet the rigidity requirement.

The side surface conformal constraint and the stirring motion (the stirring needle 14 is synchronous with the shaft shoulder) synchronously advance along with the additive manufacturing motion; the shape following restraining plates are symmetrically arranged on the side surfaces of the two sides, force is applied equivalently, and the fixed end surface is 0.5-20 mm higher than the blank.

By adopting the method, the stirring efficiency can be increased, and the blank piece can be continuously formed, stirred, formed and accurately formed. Finally, the purposes of crushing the branch crystals, fully refining the crystal grains and accurately forming are achieved.

The structure of the device adopted in the method is shown in fig. 1-4, and comprises a forming substrate 2, an additive forming blank heat source 3, a single-pass forming blank 6, a left restraining plate 15, a left driving roller 7, a left restraining plate guiding unit 17, a right restraining plate 4, a right driving roller 5, a right restraining plate guiding unit 16, a heat source center 18 and a stirring device; the stirring device comprises a stirring needle 14, a stirring rotating shaft 9, a stirring shaft shoulder 11, a stirring shaft shoulder pressing plate 12 and shaft shoulder auxiliary pressing plate supports 8, the stirring needle 14 rotates synchronously with the stirring shaft shoulder 11 along with the stirring rotating shaft 9, the relative position degree between the stirring shaft shoulder pressing plate 12 and the stirring rotating shaft 9 is rigidly fixed by the two shaft shoulder auxiliary pressing plate supports 8, the stirring shaft shoulder pressing plate 12 acts on the upper surface of a single-channel forming blank 6, the stirring shaft shoulder pressing plate blank is not wet, and the rigid constraint condition is met; the additive forming blank heat source 3 is arranged on the forming base plate 2, the single-channel forming blank 6 is arranged on the additive forming blank heat source 3, the left restraining plate 15 and the right restraining plate 4 are symmetrically arranged on two sides of the single-channel forming blank 6, the left restraining plate 15 can move along the additive manufacturing direction under the driving of the left driving roller 7 and the guiding of the left restraining plate guiding unit, and the right restraining plate 4 can synchronously advance along the additive manufacturing direction under the driving of the right driving roller 5 and the guiding of the right restraining plate guiding unit 16; the stirring motion of the stirring device advances synchronously with the additive manufacturing motion; a heat source 13 is provided at the end of the single pass of the formed blank 6.

The left restraint plate 15 and the right restraint plate 4 are synchronous with the additive setting position, are rigidly controlled and are about 1-1.5 times of the cladding height; the left and right

side restraining plates

15, 4 may provide left and right side restraining forces.

The left driving roller 7 and the right driving roller 5 are cylindrical rollers, the diameter of each cylindrical roller is 1-3 times of the thickness of a cladding single channel, and the number of rollers is more than or equal to 2; when the rollers are multiple, the center distance between two adjacent uniformly distributed driving rollers is about 1.5-5 times of the diameter of the rollers. The number of the taking rollers is related to the curvature of the forming member; the column height of the left driving roller 7 and the right driving roller 5 is about 1-1.2 times of that of the restraint plate, and the bottom ends of the left driving roller and the right driving roller are flush with the restraint plate during assembly;

the relative position degree between the shaft shoulder auxiliary pressure plate and the stirring shaft is rigidly fixed by two shaft shoulder auxiliary pressure plate supports 8, the stirring rotating shaft 9 and the stirring needle 14 keep the same rotating speed, the relative position is unchanged, the stirring rotating direction 10 can be clockwise or anticlockwise, the stirring shaft shoulder 11 and the stirring needle 14 are synchronous in position and are controlled in rotation, the stirring shaft shoulder pressure plate 12 (is not wetted with a forming material and meets rigid constraint conditions), the width of the shaft shoulder is 1-3mm narrower than that of the constraint plates on the left side and the right side and is 3-5 times of the diameter D of the stirring needle 14; the length of the shaft shoulder is 70-80% of the length of the restraint plate, and the installation position starts from the tail part of the molten pool. The thickness can meet the rigidity requirement. The heat source 13 may be a high energy beam or an electric arc; the material of the stirring pin 14 is not melted with the cladding material, the melting point is more than 500 degrees higher than that of the cladding material under the condition of ensuring the rigidity, the stirring pin 14 can stir the semi-solid metal to be formed, and can be realized by adopting a cone shape, a triangular prism shape, a column shape and a spiral shape under the condition of meeting the use rigidity and the wettability, but the radial dimension of the stirring pin 14 is not more than 50 percent of the single-pass forming width.

The heat source 13 is arranged at the left and right middle positions of the cladding surface, the right restraint plate guide unit 16 and the left restraint plate guide unit 17 are mechanically rounded, and position sensors can be arranged at the front and the rear of the clamping plate.

The center distance between the stirring pin 14 and the heat source 13 ensures that the stirring pin 14 can be in a semi-solid stirring state.

Claims

1. An apparatus for refining grains in additive manufacturing, comprising: the device comprises a forming substrate (2), an additive forming blank heat source (3), a single-channel forming blank (6), a left restraint plate (15), a left driving roller (7), a left restraint plate guide unit (17), a right restraint plate (4), a right driving roller (5), a right restraint plate guide unit (16), a heat source center (18) and a stirring device; the stirring device comprises a stirring needle (14), a stirring rotating shaft (9), a stirring shaft shoulder (11), a stirring shaft shoulder pressing plate (12) and shaft shoulder auxiliary pressing plate supports (8), the stirring needle (14) synchronously rotates with the stirring shaft shoulder (11) along with the stirring rotating shaft (9), the relative position degree between the stirring shaft shoulder pressing plate and the stirring rotating shaft is rigidly fixed by the two shaft shoulder auxiliary pressing plate supports (8), the stirring shaft shoulder pressing plate (12) acts on the upper surface of a single-channel forming blank (6), the stirring shaft shoulder pressing plate blank is not wetted, and the rigid constraint condition is met; the additive forming blank heat source is arranged on the forming base plate (2), the single-channel forming blank (6) is arranged on the additive forming blank heat source (3), the left restraining plate (15) and the right restraining plate (4) are symmetrically arranged on two sides of the single-channel forming blank (6), the left restraining plate (15) can synchronously advance along additive manufacturing movement along the additive manufacturing direction under the drive of the left driving roller (7) and the guide of the left restraining plate guide unit, and the right restraining plate (4) can synchronously advance along the additive manufacturing movement along the additive manufacturing direction under the drive of the right driving roller (5) and the guide of the right restraining plate guide unit; the stirring motion of the stirring device advances synchronously with the additive manufacturing motion; a heat source (13) is arranged at the tail end of the single-channel forming blank (6).

2. The apparatus for refining grains in additive manufacturing according to claim 1, wherein: the gyro wheel is a plurality of, along the additive manufacturing direction.

3. A method for refining crystal grains by the device for refining crystal grains in the additive manufacturing process as claimed in claim 1, wherein a method for stirring semi-solid blank by a shaft shoulder constraint stirring pin in the melting additive manufacturing process is adopted, dendrite is crushed, nucleation rate is increased, crystallization rate is improved, crystal grains are refined, meanwhile, the blank is constrained in a form of constraint along with the shape of two side surfaces, the blank is prevented from flowing and deviating from a digital model in the stirring process, and the constraint along with the shape of the side surfaces and the stirring motion synchronously advance along with the additive manufacturing motion.

4. A method for refining grains according to claim 3, wherein the side-conformal constraint is performed by using a roller + plate.

5. A method for refining grains according to claim 3, wherein the melting is operated using a plasma arc, an electric arc or an electron beam as a heat source.

6. A method of refining grains according to claim 3, wherein the additive raw material is a metal strip or wire.

7. The method for refining grains according to claim 3, wherein the stirring is performed by using a shaft shoulder-constrained stirring pin, the side surface conformal constraint is performed by using a side surface conformal constraint plate, the melting point of the material selected by the stirring pin is higher than the melting point of the forming metal by at least 500 ℃, the side surface conformal constraint plates on two sides are symmetrically arranged, the force is applied equivalently, and the fixed end surface is higher than the blank by 0.5-20 mm synchronously; the digifax requires the width of the forming surface and the molten metal strip meets the additive manufacturing requirements.

8. A method for refining grains according to claim 3, wherein when the stirring is performed by a shoulder-constrained pin, the pin has a diameter of 0.1-10 mm, the depth of stirring is 1.2-1.5 times the thickness of the in-situ forming, and the stirring speed is controlled to ensure crushing and crushing of the primary crystals and to prevent excessive flash.

9. The method of refining grains according to claim 3, wherein the pin is columnar or tapered.